Mobile phones will be banned in New South Wales public high school classrooms, recesses and lunchtimes from Term 4.
The newly elected state government says the ban delivers on a promise made during the election campaign to reduce distractions for high school students.
It will mean students must not use their phones during school hours.
They are already banned in NSW primary schools.
Premier Chris Minns said parents were worried about their children texting and using social media during class.
"I know a lot of adults who find it difficult to concentrate when a mobile phone is in front of them, so I don't know why we expect children to have that kind of discipline in them," he said.
Mr Minns said the government would not specify how schools should keep phones out of students' hands, but said locked pouches and lockers were options.
"There are low-cost and no-cost options that are available to them," Mr Minns said.
"It may be as simple as making sure mobile phones are in a student's bag and can't be taken out during the school day."
He said he recognised some children would try and get around the ban by sneaking phones to class or using laptops instead.
But he said there was evidence in other states, and in the UK, that the ban improved learning outcomes.
"In the UK the benefits were felt the highest among the students with the lowest scores," he said.
"They received double the increase in scores that the average students in their cohort were able to achieve."
Condell Park High School in Sydney's south-west has had a phone ban policy for 16 years.
Students must drop their phones off at the foyer each day, which can be accessed in an emergency.
Principal Susie Mobayed has worked at the school for 20 years and said there was less disruption.
"There is absolutely no interruption to the teaching and learning in the classroom," she said.
"Nobody's receiving calls or making calls, nobody's messaging, nobody's taking photos, and during recess and lunch, our kids are out there playing."
Ms Mobayed said the school's position was supported by parents.
"Our P&C (Parents and Citizens Association) wanted us to do this; they actually want us to ensure that their kids don't have phones because I think they struggle at home to take the phone away from their kids," she said.
Omar Salama, who is in year 12, believes phones distract from interaction among students.
"You're not going to be able to [socialise] if everyone's three feet into their phones, messaging people outside the school," he said.
Another year 12 student, Harris Nazim, said there were concerns at his previous school — where phones were allowed — of the devices being misused.
"Not just the safety of the students; it's also the safety of the teachers and the staff; you need to be a lot more cautious when you have phones," he said.
The students admitted there were attempts to smuggle phones in.
South Australia, Western Australia, Victoria and the Northern Territory have also banned phones in public high schools.
Many high schools in NSW already have bans in place and require students to put them in lock boxes or pouches at the start of the day.
